Touch screens are widely used in many portable electronic devices, for instance in PDA (Personal Digital Assistant) devices, tabletops, touch surfaces, and mobile devices. Touch screens are operable by a pointing device (or stylus) and/or by a finger. Typically the devices also comprise conventional buttons for certain operations.
3D displays capable of displaying stereoscopic images have been developed also for portable and handheld devices. Stereoscopic displays may be used to display UI items perceived by the user as three-dimensional (3D) images. The introduction of 3D displays also brings new challenges and possibilities for user interaction design.